So I have this mesh and I exported .fbx but when I did that, the mesh turned black after I applied the texture. (I UV mapped the mesh because I had applied materials to it and then uploaded it to roblox as a decal)
So I then exported it .obj and once I applied the texture this is what it looked like.
How do I get rid of the lines all over it?
Somebody, please, I don’t know how to fix this.
Did it look like that in the modeling program?
I used Blender and this is what it looks like. 
The lines appear as if it was imported in edit mode or something.
Is your texture super small or something? Could be bleeding pixels from image scaling
I don’t think thats it, but when I UV mapped it I had to shrink both UV maps because I had to duplicate the train to fix the inside, so the original train was half, and the other half of the map was the duplicated train.
Do you know the resolution of the texture before you uploaded it Roblox? To be, it looks like what was stated above about the image scaling since the lines have a staircase effect but are blurry.
What you’re looking at is the UV layout. When you model something within blender, it automatically comes with a UV layout of your model (this is what’s used for the actual texturing process). Those black lines are drawing out your vertices, and it helps navigates back to your original model when texturing.
Example:
And it looks like blender is merging both your UV layout and texture for you. Usually it’s recommend to import your UV layout separately into Photoshop, then paint on your textures.
Unfortunately I don’t use blender, but you might find these links helpful:
I would recommend looking into UV unwrapping.
Edit:
You can also try asking on the Roblox Helpers’ Discord (in le Building channel): Roblox Helpers
People on there are very nifty with Blender.
